Abrasive liquid for metal and method for polishing

ABSTRACT

An abrasive liquid for a metal comprising (1) an oxidizing agent for a metal, (2) a dissolving agent for an oxidized metal, (3) a first protecting film-forming agent such as an amino acid or an azole which adsorbs physically on the surface of the metal and/or forms a chemical bond, to thereby form a protecting film, (4) a second protecting film-forming agent such as polyacrylic acid, polyamido acid or a salt thereof which assists the first protecting film-forming agent informing a protecting film and (5) water; and a method for polishing.

This application is a Continuation application of application Ser. No.09/763,891, filed Jun. 11, 2001, which is a National Stage applicationfiled under 35 USC §371 of International (PCT) Application No.PCT/JP99/04694, filed Aug. 31, 1999.

TECHNICAL FIELD

This invention relates to a polishing solution for metal, and apolishing method, especially suited for use in polishing in the step offorming wirings of semiconductor devices.

BACKGROUND ART

In recent years, with the trend toward higher integration and higherperformance of semiconductor integrated circuits (hereinafter “LSIcircuits”), new fine-processing techniques are on development. Chemicalmechanical polishing (hereinafter “CMP”) is one of them, which is atechnique frequently used in LSI circuit fabrication steps, inparticular, in the planarizing of interlayer insulating films, theformation of metal plugs and the formation of buried wiring, in the stepof forming multi-layer wiring. This technique is disclosed in, e.g.,U.S. Pat. No. 4,944,836.

Recently, aiming at higher performance of LSI circuits, it is alsoattempted to use copper alloys as a wiring material. The copper alloys,however, make it difficult to perform the fine processing by dry etchingthat has frequently been used in the formation of conventional aluminumalloy wiring. Accordingly, what is called damascene process is employedin which copper or its alloy thin film is deposited on an insulatingfilm having grooves which are formed previously, the film standingburied in the grooves, and the copper alloy thin film other than that onthe grooves are removed by CMP to form buried wiring. This technique isdisclosed, e.g., in Japanese Patent Application Laid-open No. 2-278822.

In a common method for CMP of metals, a polishing pad is stuck onto acircular polishing surface plate (platen), the surface of the polishingpad is soaked with a polishing slurry for metal, the surface of asubstrate on which a metal film has been formed is pressed against thepad surface, the polishing platen is rotated in the state a presetpressure (hereinafter “polishing pressure ”) is applied from its backside, and hills of the metal film are removed by mechanical frictionbetween the polishing slurry and the hills of the metal film.

Polishing slurries for metal which are used in CMP are commonlycomprised of an oxidizing agent and solid abrasive particle or powderand also an oxidized-metal dissolving agent and a protective-filmforming agent which are optionally further added. What is considered tobe basic mechanism is that the metal film surface is first oxidized byoxidation and the oxide layer thus formed is scraped off by the solidabrasive grains. The oxide layer at valleys of the metal surface doesnot so much come in touch with the polishing pad, and the effect ofscrape-off by solid abrasive grains does not extend thereto, so thatwith progress of CMP, hills of the metal layer are removed and the metalmember surface become smooth. Details of the matter are disclosed inJournal of Electrochemical Society, Vol. 138, No. 11(published 1991),pages 3460-3464.

It is considered that the effect of scrape-off by solid abrasive grainsis enhanced as long as the grains of a metal oxide scraped off by thesolid abrasive grains have been dissolved in the polishing slurry by theaid of the oxidized-metal dissolving agent. If, however, the oxide layerat valleys of the metal film surface is also dissolved (hereinafter“etched”) until the metal film surface becomes uncovered, the metal filmsurface is further oxidized by the oxidizing agent. If this is repeated,the oxide layer at valleys may unwontedly be etched further, resultingin a loss of the effect of smoothing. There is such a possibility. Inorder to prevent it, a protective-film forming agent is further added.It is important to well balance the effects attributable to theoxidized-metal dissolving agent and protective-film forming agent, andit is desired that the oxide layer of the metal film surface is not somuch etched, that the grains of the oxide layer scraped off aredissolved in a good efficiency and that the polishing by CMP is at ahigh rate.

Thus, adding such oxidized-metal dissolving agent and protective-filmforming agent so as to add an effect of chemical reaction brings aboutan improvement in CMP rate (i.e., polishing rate attributable to CMP),and also can provide the effect of less damaging the metal film surfacesubjected to the CMP.

However, when the buried wiring is formed by CMP using the conventionalpolishing slurry for metal, containing solid abrasive grains, there areproblems such that (1) a phenomenon may take place in which the middleportion of the surface of buried metal wiring is isotropically corrodedto become hollow like a dish (hereinafter “dishing”), (2) polishing mars(scratches) due to the solid abrasive grains may occur, (3) acomplicated cleaning process is required for removing any solid abrasivegrains remaining on the substrate surface after polishing, and (4) theinitial cost of the solid abrasive grains themselves and the disposal ofwaste liquid brings about a high cost.

In order to keep the dishing from occurring and the copper alloy frombeing corroded during polishing and to form highly reliable LSI wiring,a method making use of a polishing solution for metal which contains anoxidized-metal dissolving agent comprised of aminoacetic acid (glycine)or amidosulfuric acid and benzotriazole (hereinafter “BTA”) is proposed.This technique is disclosed in, e.g., Japanese Patent ApplicationLaid-open No. 8-83780.

The BTA, however, has so high a protective-film forming effect that itmay cause a great decrease in not only etching rate but also polishingrate. Hence, it is demanded to use in the polishing solution for metal aprotective-film forming agent that does not cause any decrease in CMPrate.

DISCLOSURE OF THE INVENTION

The present invention provides a polishing solution for metal, and apolishing method, which can make the etching rate sufficiently low, andcan form highly reliable metal film buried patterns while maintaining ahigh CMP rate.

The polishing solution for metal of the present invention comprises anoxidizing agent for oxidizing a metal, an oxidized-metal dissolvingagent, a first protective-film forming agent, a second protective-filmforming agent different from the first protective-film forming agent,and water.

The protective-film forming agents are agents capable of formingprotective films on the metal surface.

The first protective-film forming agent may preferably be at least oneselected from nitrogen containing compounds such as ammonia,alkylamines, amino acids, imines and azoles, and salts thereof,mercaptans, glucose, and cellulose. These protective-film forming agentsare compounds capable of forming protective films by forming physicaladsorption and/or chemical linkage on the metal film surface.

The second protective-film forming agent may preferably be at least oneselected from alcohols (i.e., compounds having an alcoholic hydroxylgroup), phenols (i.e., compounds having a phenolic hydroxyl group),esters, ethers, polysaccharides, amino acid salts, polycarboxylic acidsand salts thereof, vinyl polymers, sulfonic acid and salts thereof,aromatic amines, amides, azo compounds, and molybdenum compounds. Thesesecond protective-film forming agents are compounds which assist thefirst protective-film forming agent in forming the protective film.

The oxidizing agent may preferably be at least one selected fromhydrogen peroxide, nitric acid, potassium periodate, hypochlorous acidand ozone water.

The oxidized-metal dissolving agent may preferably be at least oneselected from organic acids and ammonium salts thereof, and sulfuricacid.

In the present invention, a polishing solution for metal is provided inwhich, based on a concentration A of the first protective-film formingagent added which is necessary for exhibiting the effect of controllingthe etching rate to 10 nm/minute or lower without incorporating thesecond protective-film forming agent among the protective-film formingagents, the second protective-film forming agent is added in aconcentration lower than the concentration A so that the effect ofcontrolling the etching rate to 10 nm/minute or lower can be exhibited.More specifically, in this case, the second protective-film formingagent is a compound which enables the first protective-film formingagent, necessary for controlling the etching rate to 10 nm/minute orlower, to be added in a smaller quantity.

The polishing method of the present invention is a polishing method ofpolishing a metal film formed on the surface of a polishing object, inthe polishing solution for metal according to the present invention toremove the metal film. As the metal film to be removed, suited arecopper, copper alloys, copper oxides, copper alloy oxides and so forth.Accordingly, the present invention provides a polishing methodcomprising the step of polishing a metal film comprised of a multi-layerfilm containing at least one layer of a metal selected from copper, acopper alloy, a cooper oxide and a copper alloy oxide, to remove atleast part of the metal film.

The present invention provides a polishing solution in which the firstand second protective-film forming agents having properties differentfrom each other are used in combination so as to make the etching ratesufficiently low while maintaining the CMP rate, and a polishing methodmaking use of such a polishing solution. As the first protective-filmforming agent, usable are those capable of readily producing a chelatecomplex with copper, e.g., ethylenediaminetetraacetic acid,benzotriazole or the like. These have a very strong effect of forming ametal surface protective-film. For example, its incorporation in thepolishing solution for metal in an amount of 0.5% by weight or moremakes no CMP take place, to say nothing of etching.

On the other hand, the present inventors have discovered that the use ofthe first protective-film forming agent in combination with a secondprotective-film forming agent different from the former enables theetching rate to be sufficiently low even when the first protective-filmforming agent is added in a low concentration. Moreover, it has beenfound that the use of such a polishing solution can provide preferableproperties that the CMP rate does not so much decrease even when theetching rate decreases. In addition, they have discovered that the useof the first protective-film forming agent in combination with thesecond protective-film forming agent makes it possible to carry outpolishing at a practical CMP rate even without adding any solid abrasivegrains in the polishing solution. This is presumed to be due to thescrape-off attributable to the friction by the polishing pad, effectedin place of the effect of the scrape-off attributable to the friction bysolid abrasive grains in conventional cases.

As a value at which the etching rate is to be controlled, it has beenfound that a preferable smoothing effect is obtainable as long as it iscontrolled to 10 nm/minute or lower. As long as the decrease in CMP rateis within a tolerable range, it is preferable for the etching rate to bemuch lower. Where the etching rate can be controlled to 5 nm/minute orlower, the dishing can be kept at a level not problematic, even when theCMP is carried out in excess by, e.g., about 50% (the CMP is carried outabout 1.5 times the time necessary for removing the metal film by CMP).Where the etching rate can further be controlled to 1 nm/minute orlower, the dishing dose not come into question even when the CMP iscarried out in excess by 100% or more.

Incidentally, in the present specification, the etching rate refers to arate at which a metal film (copper film formed by sputtering) on thesurface of a polishing object is etched when the polishing object isimmersed in the polishing solution and the polishing solution is stirredat a liquid temperature of 25° C. and at a stirring speed of 100 rpm,where a difference in thickness of the metal film before and afterimmersion is calculated from the value of electrical resistance and thedifference found is divided by immersion time to determine the rate.

The CMP rate (i.e., chemical mechanical polishing rate) also refers to arate obtained when a metal film (copper film formed by sputtering) onthe surface of a polishing object is polished under conditions of apolishing pressure of 210 g/cm², a polishing object/polishing platenrelative speed of 36 m/minute and a liquid temperature of 25° C., wherea difference in thickness of the metal film before and after polishingis calculated from the value of electrical resistance and the differencefound is divided by treatment time to determine the rate.

According to the present invention, as being different from a polishingsolution making use of only the first protective-film forming agent, andwithout relying on any strong mechanical friction by solid abrasivegrains, the surface can be smoothed by CMP by the action of frictionwith a polishing pad, which is much softer than the solid abrasivegrains.

The present invention further provides a polishing method of polishing asubstrate by the use of the polishing solution for metal according tothe present invention; the substrate having valleys at its surface, anda metal film comprised of copper, a copper alloy (such ascopper/chromium) or the like being formed thereon, filling the grooveswith the film. Where such a substrate is subjected to CMP by the use ofthe polishing solution of the present invention, the metal film at hillsof the substrate is selectively removed by CMP and the metal filmremains in valleys, thus the desired conductor pattern is obtained. Thepolishing solution of the present invention substantially need notcontain any solid abrasive grains, and hence polish scratches candramatically be lessened because the CMP proceeds by the friction with apolishing pad, which is mechanically much softer than the solid abrasivegrains.

The polishing solution for metal according to the present invention hasas essential components the oxidizing agent, the oxidized-metaldissolving agent, the first protective-film forming agent, the secondprotective-film forming agent, and water.

The solid abrasive grains substantially need not be contained, but mayalso be used.

The respective components contained in the polishing solution for metalaccording to the present invention are specifically described below.

The metal-oxidizing agent may include hydrogen peroxide (H₂O₂), nitricacid, potassium periodate, hypochlorous acid, ozone water, and the like.In the case when the substrate is a silicon substrate having devices forintegrated circuits, any contamination due to alkali metals, alkalineearth metals or halides is not desirable, and hence oxidizing agentscontaining no nonvolatile component are preferred. Ozone water maygreatly cause a compositional change with time. Accordingly, among theoxidizing agents listed above, hydrogen peroxide is most preferred.However, oxidizing agents containing a nonvolatile component may be usedwhen the substrate is a glass substrate having no semiconductor devices.

The oxidized-metal dissolving agent may preferably be water-soluble one.Such a water-soluble oxidized-metal dissolving agent may include:

-   -   organic acids such as formic acid, acetic acid, propionic acid,        butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic        acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid,        4-methylhexanoic acid, 4-methylpentanoic acid, n-heptanoic acid,        n-methylhexanoic acid, n-octanoic acid, n-ethylhexanoic acid,        benzoic acid, glycoric acid, salicylic acid, glyceric acid,        oxalic acid, malonic acid, succinic acid, glutaric acid, adipic        acid, pimelic acid, maleic acid, phthalic acid, malic acid,        tartaric acid and citric acid;    -   ammonium salts such as ammonium salts of these organic acids,        ammonium persulfate, ammonium nitrate and ammonium chloride;    -   inorganic acids such as sulfuric acid and chromic acid; ammonium        complexes and the like. Any of these may be used alone or may be        used in combination.

Of these, formic acid, malonic acid, malic acid, tartaric acid andcitric acid are preferred with respect to a multi-layer film containinga metal film formed of copper, a copper alloy, a copper oxide and/or acopper alloy oxide. These acids are preferable in view of an advantagethat they can be well balanced with the first protective-film formingagent and second protective-film forming agent described later. Inparticular, with regard to malic acid, tartaric acid and citric acid,they are preferable in view of an advantage that the etching rate caneffectively be controlled maintaining a practical CMP rate.

The first protective-film forming agent may include:

-   -   ammonia;    -   amines such as alkylamines such as dimethylamine,        trimethylamine, triethylamine and propylenediamine,        ethylenediaminetetraacetic acid (hereinafter “EDTA”), sodium        diethyldithiocarbamate and chitosan;    -   amino acids such as glycine, L-alanine, β-alanine,        L-2-aminobutyricacid, L-norvaline, L-valine, L-leucine,        L-norleucine, L-isoleucine, L-alloisoleucine, L-phenylalanine,        L-proline, sarcosine, L-ornithine, L-lysine, taurine, L-serine,        L-threonine, L-allothreonine, L-homoserine, L-tyrosine,        3,5-diiodo-L-tyrosine, β-(3,4-dihydroxyphenyl)-L-alanine,        L-thyroxine, 4-hydroxy-L-proline, L-cystine, L-methionine,        L-ethionine, L-lanthionine, L-cystathionine, L-cysteic,        L-cystinic acid, L-aspartic acid, L-glutamic acid,        S-(carboxymethyl)-L-cysteine, 4-aminobutyric acid, L-asparagine,        L-glutamine, azaserine, L-arginine, L-canavanine, L-citruline,        δ-hydroxy-L-lysine, creatine, L-kynurenine, L-histidine,        1-methyl-L-histidine, 3-methyl-L-histidine, ergothioneine,        L-tryptophan, actinomycin C1, apamine, angictensin I,        angiotensin II and antipain;    -   imines such as dithizone, cuproine(2,2′-biquinoline),        neocuproine(2,9-dimethyl-1,10-phenanthroline),        vasocuproine(2,9-dimethyl-4,7-diphenyl-1,10-phenanthr oline) and        cuperazone (bicyclohexanone oxalylhydrozone);    -   azoles such as benzimidazole-2-thiol, 2-[2-(benzothiazolyl)]        thipropionic acid, 2-[2-(benzothiazolyl)] thiobutyric acid,        2-mercaptobenzothiazole, 1,2,3-triazole, 1,2,4-triazole,        3-amino-1H-1,2,4-triazole, benzotriazole,        1-hydroxybenzotriazole, 1-dihydroxypropylbenzotriazole,        2,3-dicarboxypropylbenzotriazole, 4-hydoxybenzotriazole,        4-carboxyl-1H-benzotriazole, 4-ethoxycarbonyl-1H-benzotriazole,        4-butoxycarbonyl-1H-benzotriazole,        4-octyloxycarbonyl-1H-benzotriazole, 5-hexylbenzotriazole,        N-(1,2,3-benzotriazolyl-1-methyl)-N-(1,2,4-triazolylmethyl)2-ethylhexylamine,        tolyltriazole, naphthotriazole and        bis[(1-benzotriazolyl)methyl]phosphonic acid;    -   mercaptans such as nonylmercaptan, dodecylmercaptan,        triazinethiol, triazinedithiol and triazinetrithiol; and    -   saccarides such as glucose and cellulose. Any of these may be        used alone or may be used in appropriate combination.

Of these, chitosan, ethylenediaminetetraacetic acid, L-tryptophan,cuperazone, triazinedithiol, bonzotriazole, 4-hydroxybonzotriazole,4-carboxyl-1H-benzotriazole butyl ester, tolyltriazole andnaphthotriazole are preferred in order to achieve both a high CMP rateand a low etching rate. In particular, benzotriazole and derivativesthereof are preferred. Benzotriazole derivatives may include the azoleslisted above.

The second protective-film forming agent may include;

-   -   alcohols such as 1-propanol, 2-propanol, 2-propin-1-ol, allyl        alcohol, ethylene cyanohydrin, 1-butanol, 2-butanol,        (S)-(+)-2-butanol, 2-methyl-1-propanol, t-butyl alcohol,        perfluoro-t-butyl alcohol, crotyl alcohol, 1-pentanol,        2,2-dimethyl-1-propanol, 2-methyl-2-butanol, 3-methyl-1-butanol,        S-amyl alcohol, 1-hexanol, 4-hydroxy-4-methyl-2-pentanone,        4-methyl-2-pentanol, cyclohexanol, DL-3-hexyl alcohol,        1-heptanol, 2-ethylhexyl alcohol, (S)-(+)-2-octanol, 1-octanol,        DL-3-octyl alcohol, 2-hydroxybenzyl alcohol, 2-nitrobenzyl        alcohol, 3,5-dihydroxybenzyl alcohol, 3,5-dinitrobenzyl alcohol,        3-fluorobenzyl alcohol, 3-hydroxybenzyl alcohol, 4-fluorobenzyl        alcohol, 4-hydroxybenzyl alcohol, benzyl alcohol,        m-(trifluoromethyl)benzyl alcohol, m-aminobenzyl alcohol,        m-nitrobenzyl alcohol, o-aminobenzyl alcohol, o-hydroxybenzyl        alcohol, p-hydroxybenzyl alcohol, p-nitrobenzyl alcohol,        2-(p-fluorophenyl) ethanol, 2-aminophenethyl alcohol,        2-methoxybenzyl alcohol, 2-methyl-3-nitrobenzylalcohol,        2-methylbenzylalcohol, 2-nitrophenethyl alcohol, 2-phenyl        ethanol, 3,4-dimethylbenzyl alcohol, 3-methyl-2-nitrobenzyl        alcohol, 3-methyl-4-nitrobenzyl alcohol, 3-methylbenzyl alcohol,        4-fluorophenethyl alcohol, 4-hydroxy-3-methoxybenzyl alcohol,        4-methoxybenzyl alcohol, 4-methyl-3-nitrobenzyl alcohol,        5-methyl-2-nitrobenzyl alcohol, DL-α-hydroxyethylbenzene,        o-(trifluoromethyl)benzyl alcohol, p-(trifluoromethyl)benzyl        alcohol, p-aminophenethyl alcohol, p-hydroxyphenyl ethanol,        p-methylbenzyl alcohol and S-phenethyl alcohol;    -   phenols such as 4-methylphenol, 4-ethylphenol and        4-propylphenol;    -   esters such as glycerol ester, sorbitan ester, methoxyacetic        acid, ethoxyaceticacid, 3-ethoxypropionic acid and alanine ethyl        ester;    -   ethers such as polyethylene glycol, polypropylene glycol,        polytetramethylene glycol, polyethylene glycol alkyl ethers,        polyethylene glycol alkenyl ethers, alkyl polyethylene glycols,        alkyl polyethylene glycol alkyl ethers, alkyl polyethylene        glycol alkenyl ethers, alkenyl polyethylene glycols, alkenyl        polyethylene glycol alkyl ethers, alkenyl polyethylene glycol        alkenyl ethers, polypropylene glycol alkyl ethers, polypropylene        glycol alkenyl ethers, alkyl polypropylene glycols, alkyl        polypropylene glycol alkyl ethers, alkyl polypropylene glycol        alkenyl ethers, alkenyl polypropylene glycols, alkenyl        polypropylene glycol alkyl ethers, and alkenyl polypropylene        glycol alkenyl ethers;    -   polysaccharides such as alginic acid, pectic acid, carboxymethyl        cellulose, curdlan and pullulan;    -   amino acid salts such as glycine ammonium salt and glycine        sodium salt;    -   polycarboxylic acid and salts thereof, such as polyaspartic        acid, polyglutamic acid, polylysine, polymalic acid,        polymethacrylic acid, ammonium polymethacrylate,        sodiumpolymethacrylate, polyamic acid, polymaleic acid,        polyitaconic acid, polyfumaric acid, poly(p-styrenecarboxylic        acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide,        ammonium polyacrylate, sodium polyacrylate, polyamic acid,        ammonium polyamide, sodium polyamide and polyglyoxylic acid;    -   vinyl type polymers such as polyvinyl alcohol, polyvinyl        pyrrolidone and polyacrolein;    -   sulfonic acids and salts thereof, such as ammonium methyl        taurate, sodium methyl taurate, sodium methyl sulfate, ammonium        ethyl sulfate, ammonium butyl sulfate, sodium vinyl sulfonate,        sodium 1-allyl sulfonate, sodium 2-allyl sulfonate, sodium        methoxymethyl sulfonate, ammonium ethoxymethyl sulfonate, sodium        3-ethoxypropyl sulfonate, sodium methoxymethyl sulfonate,        ammonium ethoxymethyl sulfonate, sodium 3-ethoxypropyl sulfonate        and sodium sulfosuccinate; aromatic amines such as aniline,        N,N-dimethylaniline and benzylamine; amides such as        propionamide, acrylamide, methyurea, nicontinamide, succinamide,        phenylacetamide, pyridine-4-carboxamide,        N,N′-dibenzyl-L-tartaric acid amide and sulfanilamide;    -   azo compounds such as 1,1′-azobis(cyclohexane-1-carbonitrile),        1,1′-azobis(1-acetoxy-1-phenylethane),        2,2′-azobis(2,4-dimethylvaleronitrile),        2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl        2,2′-azobis(isobutyrate), 2,2′-azobis(isobutylonitrile),        2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid,        4,4′-azobis(4-cyanovaleric acid), 4,4′-azoxyanisole,        azoxymethane, azobenzene, azoxybenzene, azodicarbonamide,        diisopropyl azodicarboxylate, di(t-butyl) azodicarboxylate,        phenazine, Marachite Green, Methyl Orange, Congo Red and Crystal        Violet; and    -   molybdenum compounds such as disodium molybdenum (VI) dihydrate        and hexaammonium heptamolybdenum (VI) tetrahydrate. Any of these        may be used alone or may be used in appropriate combination.

Where the substrate used is, e.g., a silicon substrate for semiconductorintegrated circuits, it is not desirable for it to be contaminated withalkali metals, alkaline earth metals, halides or the like, and henceacids or ammonium salts thereof are preferred. This, however, does notnecessarily apply where the substrate is a glass substrate or the like.

Of these compounds, 2-methyl-3-nitrobenzyl alcohol, polypropyleneglycol, polyaspartic acid, polymalic acid, polyacrylic acid,polymethacrylic acid, ammonium polyacrylate, ammonium polymethacrylate,polyamic acid, ammonium polyamide, polyacrylamide, methyl taurate,benzylamine, nicontinamide, sulfanilamide, Congo Red, hexaammoniumheptamolybdenum (VI) tetrahydrate are preferred in order to achieve botha high CMP rate and a low etching rate. In particular, polyacrylic acid,polymethacrylic acid, polyamic acid, ammonium polyacrylate, ammoniumpolymethacrylate, ammonium polyamide and polyacrylamide are preferred.

As the metal film to which the present invention is applied, it is amulti-layer film containing at least one selected from copper, a copperalloy, a copper oxide and a copper alloy oxide (hereinafter generically“copper alloy”).

The present invention also provides a polishing solution for metal whichhas a CMP rate of 100 nm/minute or higher and an etching rate of 10nm/minute or lower. The polishing solution having such properties hasbeen materialized for the first time by the present invention, and canbe achieved by having the metal-oxidizing agent, the oxidized-metaldissolving agent and the water and further being mixed with the firstprotective-film forming agent in combination with the secondprotective-film forming agent different from the first protective-filmforming agent.

Usable combinations of the first protective-film forming agent with thesecond protective-film forming agent are shown below in the form offirst protective-film forming agent/second protective-film formingagent. These combinations are merely shown as examples, and the presentinvention is by no means limited to these. Other combinations may alsoappropriately be used.

Combinations that can achieve the CMP rate of 100 nm/minute or higherand the etching rate of 10 nm/minute or lower may include, e.g.,cuperazone/polymalic acid, cuperazone/polyaspartic acid,cuperazone/polyacrylamide, L-tryptophan/polyacrylamide,L-tryptophan/ammonium polyacrylate, L-tryptophan/polymalic acid,benzotriazole/polyacrylamide, benzotriazole/ammonium polyacrylate,naphthotriazole/polymalic acid, naphthotriazole/2-methyl-3-nitrobenzylalcohol, triazinedithiol/polyaspartic acid, andtriazinedithiol/polyacrylamide.

Combinations that can achieve the CMP rate of 100 nm/minute or higherand the etching rate of 1 nm/minute or lower may include, e.g.,cuperazone/polyacrylamide, L-tryptophan/polyacrylamide,L-tryptophan/ammonium polyacrylate, benzotriazole/polyacrylamide,benzotriazole/ammonium polyacrylate, naphthotriazole/polymalic acid,triazinedithiol/polyaspartic acid, and triazinedithiol/polyacrylamide.

Combinations that can achieve a CMP rate of 250 nm/minute or higher andthe etching rate of 10 nm/minute or lower may include, e.g.,cuperazone/polymalic acid.

The amount in which each component is mixed is described below.

The oxidizing agent component may preferably be mixed in an amount offrom 0.003 mol to 0.7 mol, more preferably from 0.03 mol to 0.5 mol, andparticularly preferably from 0.2 mol to 0.3 mol, based on 100 g of thetotal amount of the oxidizing agent, oxidized-metal dissolving agent,first protective-film forming agent, second protective-film formingagent and water. If it is mixed in an amount less than 0.003 mol, themetal may insufficiently be oxidized, resulting in a low CMP rate. If itis in an amount more than 0.7 mol, the surface polished tends to have aroughness.

The oxidized-metal dissolving agent component in the present inventionmay preferably be mixed in an amount of from 0 mol to 0.005 mol, morepreferably from 0.00005mol to 0.0025 mol, and particularly preferablyfrom 0.0005mol to 0.0015 mol, based on 100 g of the total amount of theoxidizing agent, oxidized-metal dissolving agent, first protective-filmforming agent, second protective-film forming agent and water. If it ismixed in an amount more than 0.005 mol, the etching tends to becontrollable with difficulty.

The first protective-film forming agent may preferably be mixed in anamount of from 0.0001 mol to 0.05 mol, more preferably from 0.0003 molto 0.005 mol, and particularly preferably from 0.0005 mol to 0.0035 mol,based on 100 g of the total amount of the oxidizing agent,oxidized-metal dissolving agent, first protective-film forming agent,second protective-film forming agent and water. If it is mixed in anamount less than 0.0001 mol, the etching tends to be controllable withdifficulty. If it is in an amount more than 0.05 mol, a low CMP ratetends to result.

The second protective-film forming agent may preferably be mixed in anamount of from 0.001% by weight to 0.3% by weight, more preferably from0.003% by weight to 0.1% by weight, and particularly preferably from0.01% by weight to 0.08% by weight, based on 100 g of the total amountof the oxidizing agent, oxidized-metal dissolving agent, firstprotective-film forming agent, second protective-film forming agent andwater. If it is mixed in an amount less than 0.001% by weight, theeffect of its use in combination with the first protective-film formingagent tends not to be shown in the etching control. If it is in anamount more than 0.3% by weight, a low CMP rate tends to result.

The mechanism by which the intended effect is obtained in the polishingsolution and polishing method of the present invention is unclear. It ispresumed that the use of the first and second protective-film formingagents in combination makes them control the etching, but makes the CMPproceed without making their films function as metal surface protectivefilms against the friction by the polishing pad.

In general, the degree of polish scratches occurring in CMP depends onthe particle diameter, particle size distribution and shape of solidabrasive grains, and any decrease in layer thickness (hereinafter called“erosion”) as a result of the scrape of insulating film and anydeterioration of the smoothing effect also depend on the particlediameter of solid abrasive grains and the physical properties ofpolishing pads. When the surface of metal film, in particular, copperfilm is treated with BTA, the dishing of the metal film is considered todepend on the hardness of polishing pads and the chemical properties ofpolishing solutions. More specifically, hard solid abrasive grains arenecessary for the progress of CMP, but are not desirable for improvingthe smoothing effect in CMP and the perfectness (freeness from damagessuch as polish scratches or the like) of the surface polished by CMP.The smoothing effect is understood to actually depend more on thecharacteristics of polishing pads than on solid abrasive grains.

Thus, the present invention is considered to be very desirable for theCMP of copper alloys and besides for the formation of buried patterns byusing the same.

Incidentally, the first protective-film forming agent has the action offorming a strong protective film on the metal surface. For example,where the copper alloy film surface is exposed to a solution containingBTA, it is considered that a film of polymeric complex compound havingas the main skeleton a structure of Cu (I) BTA or Cu(II) BTA is formedas a result of the reaction of copper (Cu) or an oxide thereof with BTA.The film thus formed is fairly so tough that, when a polishing solutionfor metal is used which contains 0.5% by weight of BTA, the film isusually little polished even where solid abrasive grains are containedin the polishing solution.

On the other hand, where the polishing solution for metal is preparednot using the first protective-film forming agent and using only thesecond protective-film forming agent alone, it is difficult especiallyto control the etching rate, ensuring no sufficient protective effect.

Thus, the first protective-film forming agent and the secondprotective-film forming agent have their action different from eachother, and different type of protective films are formed in accordancewith the type of protective-film forming agents. The present inventionis based on a new discovery that the use of the first and secondprotective-film forming agents in combination enables achievement ofboth the controlling of etching rate and the maintaining of CMP rate,and moreover even makes it unnecessary to rely on the strong friction bysolid abrasive grains.

BEST MODES FOR PRACTICING THE INVENTION

The present invention will be described below by giving Examples. Thepresent invention is by no means limited by these Examples.

EXAMPLES 1 TO 12, COMPARATIVE EXAMPLES 1 TO 5

—Preparation of Polishing Solutions—

To 0.15 part by weight of DL-malic acid (a guaranteed reagent), 70 partsby weight of water was added to make a solution. To the solution formed,a solution prepared by adding 0.2 part by weight of the firstprotective-film forming agent in 0.8 part by weight of methanol wasadded, and thereafter 0.05 part by weight of the second protective-filmforming agent was further added, finally followed by addition of 33.2parts by weight of hydrogen peroxide water (a guaranteed reagent, anaqueous 30% solution) to obtain a polishing solution for metal. Herein,protective-film forming agents used in each Example and ComparativeExample are shown in Table 1.

Next, using the polishing solution thus obtained, polishing objects werepolished. Polishing conditions were as follows:

—Polishing Conditions—

Polishing object substrate: A silicon substrate with a copper filmformed in a thickness of 1 μm.

Polishing pad: IC1000 (available from Rodel Co.).

Polishing pressure: 210 g/cm².

Substrate/polishing platen relative speed: 36 m/min.

—Polished Article Evaluation Items—

CMP rate: A difference in layer thickness of the copper film before andafter CMP was determined by calculation from the value of electricalresistance and the difference found was divided by treatment time todetermined the rate. Treatment time was set to be 1 minute.

Etching rate: The same substrate as the above polishing object substratewas separately prepared, and was immersed in the polishing solution withstirring (stirring speed: 100 rpm) at room temperature (25° C.), where adifference in layer thickness of the copper film before and afterimmersing was calculated from the value of electrical resistance and thedifference found was divided by treatment time to determined the rate.Treatment time was set to be 10 minute.

In order to evaluate actual CMP performance, grooves of 0.5 μm deep wereformed in an insulating layer and a copper film was formed by knownsputtering, followed by known heat treatment to obtain a film-buriedsilicon substrate, which was also used as a substrate to carry out CMP.Whether or not any erosion and polish scratches had occurred wasexamined by visual observation, optical-microscopic observation andelectron microscopic observation of the substrate having been polishingby CMP. As the result, neither erosion nor polish scratch was seen tohave occurred. The results of evaluation on the CMP rate and etchingrate in Examples 1 to 11 and Comparative Examples 1 to 5 are shown inTable 1.

EXAMPLE 13

To 0.15 part by weight of DL-malic acid (a guaranteed reagent), 70 partsby weight of water was added to make a solution. To the solution formed,a solution prepared by adding 0.1 part by weight of BTA in 0.8 part byweight of methanol was added, and thereafter 0.025 part by weight ofammonium polyacrylate was further added in the form of an aqueous 40%solution, finally followed by addition of 33.2 parts by weight ofhydrogen peroxide water (a guaranteed reagent, an aqueous 30% solution)to obtain a polishing solution for metal. In the present Example, theDL-malic acid, an organic acid having a high solubility in water, wasused as the oxidized-metal dissolving agent, and the water-soluble,ammonium polyacrylate was used as the second protective-film formingagent.

Using this polishing solution, CMP was tested under the same conditionsas in Example 1. As the result, the CMP rate was 287 nm/minute and theetching rate was 3.6 nm/minute, both showing good results. However, asto the substrate having the groove pattern formed therein, when it waspolished by CMP in excess by 50% beyond the CMP time necessary forremoving the film by CMP in a stated thickness, the electron microscopicobservation revealed that the dishing occurred in a depth of about 200nm at grooves of 10 μm wide (the part serving as buried wiring). Inorder to control the dishing to a depth of 100 nm or less, it wasnecessary to keep the excess CMP time within 20%. Erosion and polishscratch were seen not to have occurred.

EXAMPLE 14

To 0.15 part by weight of DL-malic acid (a guaranteed reagent), 70 partsby weight of water was added to make a solution. To the solution formed,a solution prepared by adding 0.2 part by weight of BTA in 0.8 part byweight of methanol was added, and thereafter 0.125 part by weight ofammonium polyacrylate was further added in the form of an aqueous 40%solution, finally followed by addition of 33.2 parts by weight ofhydrogen peroxide water (a guaranteed reagent, an aqueous 30% solution)to obtain a polishing solution for metal. In the present Example, theDL-malic acid, an organic acid having a high solubility in water, wasused as the oxidized-metal dissolving agent, and the water-soluble,ammonium polyacrylate was used as the second protective-film formingagent.

Using this polishing solution, CMP was tested under the same conditionsas in Example 1. As the result, the CMP rate was as high as 185nm/minute and the etching rate was as low as 0.2 nm/minute. Also, as tothe substrate having the groove pattern formed therein, too, it waspolished by CMP under the same conditions as the above CMP and theobservation was made in the same manner as the above, where the dishingwas in a depth of 50 nm or less even when the CMP was carried out inexcess for the time corresponding to 50%, and neither erosion nor polishscratch was seen to have occurred.

EXAMPLE 15

A polishing solution for metal was prepared in the same manner as inExample 14 except that the DL-malic acid was replaced with DL-tartaricacid. The CMP was tested in the same manner as in Example 1. As theresult, the polishing rate was as high as 194 nm/minute and the etchingrate was 0.8 nm/minute. Also, the same substrate having the groovepattern formed therein as that of Example 13 was polished and thereafterthe substrate surface was observed, where the dishing in the case whenthe CMP was carried out in excess for the time corresponding to 50% wasin a depth of about 70 nm, and neither erosion nor polish scratch wasseen to have occurred.

EXAMPLE 16

A polishing solution for metal was prepared in the same manner as inExample 13 except that the DL-malic acid was replaced with citric acid.The CMP was tested in the same manner as in Example 1. As the result,the CMP rate was as high as 213 nm/minute but the etching rate was at alittle inferior level of 4.6 nm/minute. Also, the same substrate havingthe groove pattern formed therein as that of Example 13 was polished byCMP in excess for the time corresponding to 30% and thereafter thesubstrate surface was observed, where the dishing was in a depth ofabout 150 nm or less, and neither erosion nor polish scratch was seen tohave occurred.

COMPARATIVE EXAMPLE 6

A polishing solution for metal was prepared in the same manner as inExample 13 except that the ammonium polyacrylate was not added. The CMPwas tested in the same manner as in Example 1. As the result, the CMPrate was at only a little inferior level of 140 nm/minute, but theetching rate was as inferior as 10.3 nm/minute. Also, the same substratehaving the groove pattern formed therein as that of Example 13 waspolished by CMP in excess for the time corresponding to 30% andthereafter the substrate surface was observed, where the dishing was ina large depth of about 300 nm. Erosion and polish scratch were notobservable.

COMPARATIVE EXAMPLE 7

A polishing solution for metal was prepared in the same manner as inExample 13 except that the ammonium polyacrylate was not added and thebenzotriazole, added in an amount of 0.1 part by weight, was added in alarger amount of 0.2 part by weight. Using this polishing solution, theCMP was tested in the same manner as in Example 1.

As the result, the etching rate was as good as 2.4 nm/minute, but theCMP rate was as inferior as 93 nm/minute. Also, the same substratehaving the groove pattern formed therein as that of Example 13 waspolished by CMP in excess for the time corresponding to 30% andthereafter the substrate surface was observed. As the result, thedishing was in a depth of about 150 nm, a value not well satisfiable.This was presumably because, although the etching rate was low, the CMPrate was also so low that it took a long time for the CMP. Erosion andpolish scratch were seen not to have occurred.

As can be seen from these Examples and Comparative Examples, the effectof controlling the etching rate to 10 nm/minute or less by adding onlythe first protective-film forming agent in a stated concentration can beachieved by using the second protective-film forming agent incombination, even when the first protective-film forming agent is usedin a lower concentration, also showing the effect of maintaining ahigher CMP rate. This makes it possible to keep the dishing, erosion andpolish scratches from occurring and also to form highly reliable buriedpatterns at a high CMP rate.

POSSIBILITY OF INDUSTRIAL APPLICATION

As described above, according to the present invention, the etching ratecan be made sufficiently low, and highly reliable buried patterns can beformed maintaining a high CMP rate.

1. A polishing solution for polishing a metal film surface, comprising:(1) an additive which is capable of etching the metal film surface at anetching rate of 10 nm/minute or lower, (2) a protective film-formingagent which, in combination with said additive, is capable of removingthe metal film surface by chemical mechanical polishing at a polishingrate of at least 100 nm/minute and an etching rate of not more than 10nm/minute, and (3) water, wherein said additive is a combination of afirst material which is an oxidizer of metal of the metal film surface,thereby forming an oxide of the metal, a second material which dissolvesthe oxide of the metal, and another protective film-forming agent (a)having properties different from those of said protective film-formingagent, and (b) exhibiting an effect of controlling the etching rate tonot more than 10 nm/minute without incorporating said protectivefilm-forming agent, said protective film-forming agent and said anotherprotective film-forming agent to a ether controlling etching rate, whilemaintaining chemical mechanical polishing rate, of the metal filmsurface, to be the polishing rate of at least 100 nm/minute and theetching rate of not more than 10 nm/minute.
 2. The polishing solutionaccording to claim 1, consisting essentially of said additive, saidprotective film-forming agent and water.
 3. The polishing solutionaccording to claim 1, wherein said (2) protective film-forming agent isselected from the group consisting of compounds having an alcoholic orphenolic hydroxyl group, esters, ethers, polysaccharides, amino acidsalts, polycarboxylic acids, polycarboxylates, vinyl polymers, amides,azo compounds and molybdenum compounds.
 4. The polishing solutionaccording to claim 1, wherein said (2) protective film-forming agent isat least one selected from the group consisting of polyacrylic acids,polymethacrylic acids, polyamic acids, ammonium polyacrylates, ammoniumpolymethacrylates, ammonium polyamides and polyacrylamides.
 5. Thepolishing solution according to claim 1, which is adapted to polish ametal film surface including a material that contains at least one ofcopper, a copper alloy, a copper oxide and a copper alloy oxide.
 6. Apolishing solution for polishing a metal film surface, comprising: (1)an additive which is capable of removing metal of said metal filmsurface by chemical mechanical polishing, (2) a first protectivefilm-forming agent, (3) a second protective film-forming agent havingproperties different from those of the first protective film-formingagent, and (4) water, wherein a combination of the first protectivefilm-forming agent and the second protective film-forming agent controlsetching rate, while maintaining chemical mechanical polishing rate, ofthe metal.
 7. The polishing solution according to claim 6, wherein saidadditive is a combination of another protective film-forming agent and amaterial that oxidizes metal of the metal film surface.
 8. The polishingsolution according to claim 6, said solution being capable of removingthe metal film surface by chemical mechanical polishing at a polishingrate of at least 100 nm/minute and at an etching rate of at most 10 nm/minute.
 9. The polishing solution according to claim 6, consistingessentially of said additive, said first protective film-forming agent,said second protective film-forming agent and water.